Prelude: Economics as Evolutionary Science

1
Prelude Economics as Evolutionary Science

• Economists have been unwitting creationists
• Theory takes axiomatic approach to description of
  human nature
• Axioms are typically quite arbitrarily selected
• Platonic rationality
• Behavioral this or that
• Standard defense of ideal rationalityHow else to
  find structure?
• Proposed answer Evolution

2
Will Darwinian thinking change economics?

• I am betting that it will and that this will
  engage economics much more deeply in the other
  biological and social sciences.

3
Central Features of Evolutionary Economics

• Evolution of Fundamental Preferences
• Selfishness vs altruism
• Concern for relatives
• Time Preference
• Attitudes toward risk
• Evolution of rationality itself
• Evolution of institutions and beliefscultural
  evolution
• Group selection versus individual selection

4
Evolutionary Economics of the Family

• There is selection for behavior that maximizes
  reproductive success.
• Broadly true whether transmission is genetic or
  cultural
• Marital institutions
• Inheritance and support of the elderly
• Fraternal cooperation, sibling rivalry,
  parent-offspring conflict

5
Does Mother Nature Punish Rotten Kids?

6
A Cautionary Tale for Bad Children

• Carl Bergstrom
• Biology Department,
• University of Washington
• Ted Bergstrom
• Economics Department,
• UC Santa Barbara

7
Theories of Parent-Offspring Conflict in Biology

• Genetic-based conflict of interest
• Hamiltons rule implies
• In sexually reproducing species, individuals
  care half as much about their siblings as about
  themselves.
• Parents care equally about each of their
  children.
• Parents quarrel with their children about
• Dont be so selfish.

8
The Parental Interest View

• Biologist, Richard Alexander argues that
• Evolution selects for offspring that act to
  maximize their parents reproductive interest.
• Economist, Gary Beckers Rotten Kid Theorem
  reaches similar conclusion.

9
Alexanders arguments

• Animals who are overly greedy as children, will
  suffer the evolutionary penalty of having
  children that are overly greedy.
• Counter (Sexual reproduction does not
  produce identical copies.)
• 2) Parents are bigger, stronger, smarter.
• Counter Extortion

10
Parable of the Bleating Lamb

• A Ewe lives for two years and has one lamb each
  year.
• She weans her first lamb at some age x.
• The first lambs own survival probability is an
  increasing function of x.
• The earlier she weans, the stronger the ewe will
  be when she bears her second lamb, so the second
  lambs survival probability is a decreasing
  function of x.

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Survival Probability Tradeoff
Lamb 2

M
L1
Lamb 1
12
Opponents and Allies

• Ewe wants to maximize sum of survival
  probabilities.
• Lamb 1 wants to maximize a weighted average of
  own and Lamb 2s survival probability, with twice
  as big a weight for self.
• Lamb 2 wants to maximize weighted average with
  greater weight for self. But Lamb 2 is a passive
  player in this game.
• Mother loves firstborn, but their interests are
  partly in conflict.

13
Finding preferred points
Lamb 2
L2

M
L1
Lamb 1
14
Genetic foundations of behavior

• Suppose that sheep have genes that tell them
  what to do when they are lambs and other genes
  that tell them what to do when they are mothers.
• Suppose (temporarily) that these genes are not
  linked, so that simultaneous mutations in the
  two behaviors are hard to maintain.

15
The Power of those who are Weak but Loved by the
Strong

• Lamb can not throw down its mother and force it
  to nurse?
• Ewe is faster, stronger, smarter.
• What can lamb do?
• What do small children do?
• Bleat really loudly.
• What is lamb saying?

16
Wolf, Wolf, Mom Neglects Me!
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First-borns preferred Equilibrium

• Suppose that genes that command firstborn
  lambs tell them to call the wolf unless they can
  nurse to their preferred age.
• In the same population, mothers are soft and
  nurse the firstborn whenever it bleats.
• This is an equilibrium.
• A mutant Mom who is hard-nosed will lose her
  babies to the wolves. Her traits will not be
  passed on.
• Mutant first-born who are less demanding will not
  pass on their genes as often as the greedier
  first-born.

18
Mothers preferred Equilibrium

• Suppose that genes that command firstborn lambs
  tell them to nurse when mother offers and not to
  complain.
• And the genes controlling maternal behavior tell
  Mom to be hard-nosed. If lamb calls the wolf
  when it is older than mom-optimal weaning age,
  she ignores bleats and lets it take its chances
  with the wolf.
• This is an equilibrium.
• Mutant lamb who calls wolf is likely to be eaten
  and less likely than normal lambs to pass on his
  genes.
• Mutant mom who is less hard-nosed has fewer total
  offspring.

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Two possible equilibria

• Demanding lambs, compliant moms
• Pliant lambs, Hard-nosed Moms
• Both are evolutionary equilibria. The second
  equilibrium is more efficient in the sense that
  it reproduces more rapidly given the
  availability of resources.

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Linked Genes

• Suppose that genes that control maternal
  behavior and first-born behavior are closely
  linked, so that if an animal gets two
  mutations, one in each locus, these mutant genes
  are not likely to separate in genetic
  recombination.
• Then genetic combination, hard-nosed mom, pliant
  lamb is likely to stick together and will
  eventually outperform soft mom, demanding lamb.
  

21
Cross-over illustrated
Soft Mom
Demanding Kid

Pliant Kid
Tough Mom
A Fatal combination (but nice for wolves)
22
Conclusion

• Whether the Becker-Alexander conjecture holds
  true, depends on degree of genetic linkage
  between genes for maternal behavior and those for
  firstborn behavior.